Since the metered dose pressurised inhaler was introduced in the mid-1950's, inhalation has become the most widely used route for delivering bronchodilators, offering a rapid onset of action and a low instance of systemic side effects. More recently, inhalation from a pressurised inhaler has been a route selected for the administration of other drugs, e.g., ergotamine, which are not primarily concerned with the treatment of a bronchial malady.
The metered dose inhaler is dependent upon the propulsive force of a propellant system used in its manufacture. The propellant generally comprises a mixture of liquified chlorofluorocarbons (CFC's) which are selected to provide the desired vapour pressure and stability of the formulation. Propellants 11, 12 and 114 are the most widely used propellants in aerosol formulations for inhalation administration.
In recent years it has been established that CFC's react with the ozone layer around the earth and contribute towards its depletion. There has been considerable pressure around the world to reduce substantially the use of CFC's, and various Governments have banned the "non-essential" use of CFC's. Such "non-essential" uses include the use of CFC's as refrigerants and blowing agents, but heretofore the use of CFC's in medicines, which contributes to less than 1% of the total use of CFC's, has not been restricted. Nevertheless, in view of the adverse effect of CFC's on the ozone layer it is desirable to seek alternative propellant systems which are suitable for use in inhalation aerosols or an inhaler which is capable of delivering drugs in such an efficacious manner without employing an aerosol propellant.
Apparatus for atomising liquid, such as, liquid fuel, water, liquid drug and recording medium are disclosed, for example, in U.S. Pat. Nos. 3,812,854, 4,159,803, 4,300,546, 4,334,531, 4,465,234, 4,632,311, 4,338,576 and 4,850,534 and International Patent Application No. WO/8906147.
The atomising apparatus disclosed in U.S. Pat. Nos. 4,465,234 and 4,632,311 comprises a body having a chamber into which liquid is supplied, a nozzle member secured to the body and forming part of a wall defining the chamber, the nozzle member having at least one nozzle opening therethrough, and vibrator which is either a separate element forming part of a wall defining the chamber or is secured to the nozzle member to cause vibration thereof, such that, in use, in response to the vibrator, liquid in the chamber is cyclically pressurised, causing liquid to be periodically expelled through the nozzle opening(s) as atomised droplets. The apparatus additionally comprises a reservoir of liquid positioned below the chamber and a suction pump in communication with the chamber via an air vent pipe for sucking liquid into the chamber. The pump is de-energised after operation to drain liquid to leave the chamber dry during non-working periods to prevent the otherwise solid substances from clogging the nozzle openings.
U.S. Pat. No. 4,533,082 discloses an arrangement for discharging liquid droplets which is useful in applications such as fuel burners and printers, the arrangement comprises a housing including a chamber for holding liquid therein having an intake port connected to a liquid supply container, a vibrating member secured to the housing in pressure transmitting relation with the liquid in the chamber. The vibrating member is formed with at least one nozzle opening therein through which the liquid is discharged forwardly of the housing. A piezo-electric transducer is secured to the vibrating member for inducing a rearward displacement therein to discharge a small quantity of liquid through the nozzle opening.
U.S. Pat. Nos. 4,338,576 and 4,850,534 disclose a nebuliser which pumps up water and mists the pumped up water comprising an elongated main body with a centre hole for water passage, and piezoelectric vibration elements together with electrodes for energising the same mounted on the main body. The vibration elements are water-proofed, with the nebuliser itself supported by a flange on a water-proof member, which flange is on a plane on which a centre electrode is positioned. Upon vibration of the elements, water is pumped up through the inlet of the main body and dissipated into the air through the outlet of the main body. Preferably, the inlet and the outlet are removable from the main body and the inlet coated with a thin hard film. The outlet is preferably covered with a mesh, or at least an opening of the outlet is covered, for preventing the release of water that has not been converted to mist.
British Patent Application No. 2240494A, published 7th Aug., 1991, discloses a dispensing apparatus comprising a housing defining a chamber receiving in use a quantity of liquid to be dispensed, the housing comprising a perforate membrane which defines a front wall of the chamber and which has a rear face contacted by liquid in use, the apparatus further comprising vibrating means connected to the housing and operable to vibrate the perforate membrane to dispense droplets of liquid through the perforate membrane, wherein the housing comprises an annular member having a relatively thin inner annular portion connected to the perforate membrane and a relatively thick outer annular portion connected to the vibrating means.